Smallest black hole proves a giant find for science

April 3, 2008 12:00 am

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By , WASHINGTON, April 3 – The discovery in our own galaxy of the smallest black hole known in the universe is a feather in the cap for NASA, but it will present new challenges to future space travelers who may venture too close.

Tiny but intense, with a mass 3.8 times that of the sun and a diameter of only 15 miles (24 kilometers), this black hole in the Milky Way galaxy "is really pushing the limits" of our understanding of the phenomenon, according a NASA scientist from Goddard Space Flight Center in Maryland.

"For many years astronomers have wanted to know the smallest possible size of a black hole, and this little guy is a big step forward toward answering that question," said Nikolai Shaposhnikov in a statement by NASA.

He and colleague Lev Titarchuk made the discovery with the aid of NASA’s Rossi X-ray Timing Explorer satellite, and presented the findings earlier this week at an American Astronomical Society conference.

A black hole, which can form when a star collapses in on itself to infinite density, sucks in anything in its gravitational pull, including light. Supermassive or stellar-mass black holes can be billions of times the mass of our sun.

The latest black hole was discovered alongside a normal star in a binary system called XTE J1650-500, named for its coordinates in the constellation Ara. The system was discovered in 2001.

Despite its pint-size, this new record-holder packs an astronomical wallop that should force future space travelers in Earth’s galaxy to take note, Shaposhnikov said. Small black holes exert a force comparatively far beyond that of larger black holes found at the center of galaxies.

"If you ventured too close to J1650’s black hole, its gravity would tidally stretch your body into a strand of spaghetti," Shaposhnikov said.

The black hole cannot be observed directly, but is detected by its effect on its surroundings. Scientists observe matter trapped in its powerful gravity spiraling inward and getting hotter before being swallowed up.

Black holes also emit massive quantities of X-rays of intensity that varies in a pattern that repeats itself over a nearly regular interval, called a quasi-periodic oscillation (QPO).

Shaposhnikov and Titarchuk used the QPO frequency to determine the black hole’s mass — 3.8 times that of the sun — with a margin of error half the sun’s mass. The result was below the previous smallest black hole mass record of 6.3 times that of the sun.

The black hole’s tiny mass approaches the limits astronomers have predicted for such an object, making it very important to research in fundamental physics.

Below some unknown critical threshold, a dying star should produce a neutron star instead of a black hole. Astronomers think the boundary between black holes and neutron stars lies somewhere between 1.7 and 2.7 solar masses (330,000 times Earth’s mass).

Knowing this boundary is crucial for understanding how matter behaves under extraordinarily high density.